Which sequence correctly describes the electron flow from water to NADP+ in photosynthesis?

Which sequence correctly describes the electron flow from water to NADP+ in photosynthesis?

• A. Water → NADP+ → PSII → PSI → Cytochrome b6f → plastocyanin → NADP+ reductase → NADPH
• B. Water → PSI → PSII → plastocyanin → cytochrome b6f → NADP+ reductase → NADPH
• C. Water → PSII → cytochrome b6f → plastocyanin → PSI → NADP+ reductase → NADPH
• D. Water → PSII → NADP+ → PSI → Cytochrome b6f → NADP+ reductase → NADPH

Answer: (C)

In the light reactions, electrons move from water, which is split at PSII, through the electron transport chain to NADP+. After PSII, electrons pass through the plastoquinone pool to the cytochrome b6f complex, then to plastocyanin, which carries them to PSI. Light energy at PSI excites P700 and drives electrons to ferredoxin, which donates them to NADP+ via ferredoxin-NADP+ reductase to form NADPH. So the sequence that matches this flow is water → PSII → cytochrome b6f → plastocyanin → PSI → NADP+ reductase → NADPH. The other options place components in the wrong order (such as activating PSI before PSII or reducing NADP+ too early), which doesn’t reflect how electrons travel through the thylakoid membrane.

In the light reactions, electrons move from water, which is split at PSII, through the electron transport chain to NADP+. After PSII, electrons pass through the plastoquinone pool to the cytochrome b6f complex, then to plastocyanin, which carries them to PSI. Light energy at PSI excites P700 and drives electrons to ferredoxin, which donates them to NADP+ via ferredoxin-NADP+ reductase to form NADPH. So the sequence that matches this flow is water → PSII → cytochrome b6f → plastocyanin → PSI → NADP+ reductase → NADPH. The other options place components in the wrong order (such as activating PSI before PSII or reducing NADP+ too early), which doesn’t reflect how electrons travel through the thylakoid membrane.